1. Field of the Invention
The invention relates to signal processing, and particularly but not exclusively to the processing of speech signals in a teleconferencing system.
2. Description of the Related Art
In teleconferencing applications, it is known for a plurality of users to be interconnected by means of a teleconferencing switch, such that the users can talk to each other and listen to each other, typically from remote locations. A user typically connects to a teleconferencing system using a telephone handset apparatus, but other means such as a personal computer may be used.
When speaking, a user's voice is detected by a microphone of a suitable apparatus, such as a telephone handset, and the thus detected speech signal is provided as an input to a teleconferencing switch, and the speech then broadcast to all participants of the telephone conference.
Whilst a user's voice is detected by the microphone, the microphone also detects background noise. Such background noise may, for example, be noise within the speaker's immediate environment, such as office noises including fans and such like, or external noises such as traffic noise. Generally it is desirable to have some background noise to provide a level of ‘comfort’ to listeners in the telephone conference. It is desirable, nevertheless, to minimize background noise such that the listener in the teleconference does not hear ‘noise dominated’ speech. The elimination or minimization of noise is therefore a problem which needs to be addressed.
A speech signal delivered to the input of a teleconferencing switch also typically includes undesirable transients. Transients may become present in the speech signal due to, for example, switching taking place in the system as the speech signal is routed to the teleconferencing switch. Generally the transients can be considered to be electrical noise, and are manifested as spikes in the speech signal.
Transients could also be caused by audio sources, for example pens clicking on tables where a microphone may be situated, light switches being turned on/off, doors clicking shut etc.
These spikes caused by transients translate to sound heard by a listener in the teleconferencing system, and are also a problem which needs to be addressed.
The envelope of a speech signal provided to a teleconferencing switch generally comprises portions or segments of speech, which segments are defined by a rising edge and a falling edge. Where a speaker pauses, even only briefly, in speaking, this may be sufficient to define a separation between two speech segments. In a typical teleconferencing system, which may have only a simple threshold cutoff, such pause will result in the user's speech being cut-off during the pause, giving the impression that the speaker has finished. This is undesirable, as it does not provide a true listening experience for the listener, as the listener may not detect from the heard speech that this is simply a ‘live’ pause and the speaker is continuing. This does not provide a listener with a listening experience which approximates to being in the same room as the speaker. This is a further problem to be addressed.
In teleconferencing speech when a user finishes speaking there is typically an almost instantaneous cut-off of the speech signal from the speaker, which can appear abrupt to a listener. This does not provide a listener with a listening experience which would be similar to that of being in the same room as the speaker. This abrupt cut-off is a yet further problem to be addressed.
It is an aim of the invention to address one or more of the above-stated problems.